Method, mobile station and radio communications system for controlling security-related functions for call handling
The invention relates to a method, a mobile station and a radio communications system for controlling security-related functions for call handling as claimed in the precharacterizing clause of patent claims 1, 6 and 7.
Radio communications systems, such as the GSM Standard (Global System for Mobile Communication) mobile radio system, carry out information transmission using an air interface on which connections can be set up, cleared and maintained between mobile stations and network devices in a communications network. Mobile-radio-specific functions are carried out during call handling, including security-related functions such as subscriber authentication and the secrecy function. Access authorization for a radio subscriber to the communications network is checked by means of the subscriber authentication process which is normally started when a connection is set up between a mobile station and the communications network. The secrecy function is based on ciphering the information to be transmitted via the air interfacexe2x80x94in particular the user information. A ciphering procedure is initiated at the network end by sending a ciphering request to the mobile station, to which the mobile-station end responds by transmitting information which has already been ciphered. The security-related functions for the GSM Standard radio communications system are described, for example, in xe2x80x9cNetzxc3xcbersicht GSMxe2x80x9d [GSM network overview], Siemens AG, 1995, Chapter 3.4.2, pages 114 et seq.
The above procedure is based on the principle that the mobile station trusts the communications network, that is to say the security-related functions cannot be influenced by it. For connections which arrive at or originate from a mobile station, this means that deliberate interception is possible, for example by means of special intervention in the air interface, see the prior Patent Application P 19749388.2xe2x80x94without the mobile station being able to prevent this. In the case of the solution according to the prior patent application, the mobile station is, specifically, forced to set up an unciphered connection.
The invention is based on the object of specifying a method, a radio communications system and a mobile station of the type mentioned in the introduction, by means of which it is reliably possible to prevent interception of connections on the air interface.
This object is achieved according to the invention by the method having the features of patent claim 1, the radio communications system having the features of patent claim 6, and the by the mobile station having the features of patent claim 7. Advantageous developments of the invention can be found in the dependent claims.
Based on the known method and radio communications system for controlling the security-related functions for call handling with subscriber authentication and secrecy of the information, the ciphering request having an identifier is received and evaluated by the mobile station in order to determine whether the communications network wishes to have connections on the air interface with ciphered information or with unciphered information. In this case, the mobile station can be switched under subscriber control to an operating mode in which the connection is terminated if the received identifier allows connections with unciphered information.
The mobile station according to the subject matter of the invention comprises a control unit for evaluation of an identifier which is sent by the communications network and indicates whether the communications network wishes to have connections on the air interface with ciphered information or with unciphered information. Furthermore, the mobile station can be switched under subscriber control to an operating mode in which the control unit allows termination of the connection if the received identifier allows connections with unciphered information. The invention ensures that the connections on the air interface contain only ciphered information, otherwise termination of the connection from the mobile station end is threatened. In consequence, the mobile station has the capability to suppress or avoid interception of connections with unciphered information, under subscriber control, and thus no longer needs to leave it to the communications network to allow unciphered information transmission and to initiate corresponding connections.
One advantageous development of the invention provides for a message to clear the connection to be sent by the mobile station via the air interface to the communications network. The transmission of a clear message means that the communications network is informed directly and immediately of the termination of the connection by the mobile station.
One alternative development of the invention provides for the transmitting/receiving unit for transmitting and receiving radio signals to be temporarily switched off by the mobile station in order to signal to the communications network that the connection has been terminated.
One particularly simple, but very effective and user-friendly, option for switching the mobile station under subscriber control to the operating mode is for a special station key to be provided on the mobile station.
A development of the invention as an alternative to or in addition to this provides for the mobile station to be switched under subscriber control to the operating mode by means of input operationsxe2x80x94preferably under menu control.